In recent years, techniques for converting image information into electrical signals to be transmitted or stored or to be reproduced on a CRT have been extensively developed. Along with this, the demand for hard copies from such image information has increased, and various means of obtaining hard copies have been suggested. However, many of these hard copies are poor in image quality, and in particular the image quality of all color hard copies is not comparable with that of prints using current color papers. As means of providing a hard copy having high image quality, for example, Pictrography (trade name), which is manufactured by Fuji Photo Film Co., Ltd., and which uses an LED scanning exposure system as a system for the thermal development dye diffusion of a silver halide, can be mentioned.
On the other hand, due to the progress made in silver halide photographic materials and compact simple rapid-development systems (e.g., mini-lab systems), printed photographs of quite high image quality are supplied relatively easily and inexpensively in a short period of time. Therefore, there is very high demand for a hard copy material that can form high image quality as a hard copy of image information; that is inexpensive for such use; that can be processed simply and rapidly; and that can give stable performance.
In general, the method of obtaining a hard copy from electrical signals takes a scanning exposure system, wherein generally pieces of image information are successively picked up and exposed, and accordingly a photographic material suitable therefore is required. When a hard copy is to be obtained rapidly using a silver halide photographic material, it is required to shorten both the time of scanning exposure and the time of the development processing step. To shorten the time of scanning exposure, the exposure time per picture element has to be shortened as much as possible by using a light source high in output. It has become to be able to control the scanning exposure time in such a short time as 10.sup.-7 sec or below per picture element by advance of modulation controlling technique for scanning exposure light source. However, with respect to silver halide emulsion grains, it is well known that, as the exposure intensity becomes higher and the exposure time becomes shorter, development activity of the latent image formed by the exposure becomes weaker, the developing speed becomes slower, and the change of the photographic properties due to a change in the processing solution becomes greater. Further, in order to make the development processing step simple and rapid, it is required to use a silver halide emulsion that has a high silver chloride content, as described in WO 87/04534. However, the use of such a silver halide emulsion having a high silver chloride content results in a further increase in the change of the photographic properties due to a change in the processing solution with short, high-intensity exposure, in comparison with silver bromide emulsions and silver bromochloride emulsions that have a low silver chloride content. In addition, if the time of the development processing step is shortened further, the change of the photographic properties due to a change in the processing solution increases further. Further, it has been found that the fluctuation of photographic properties due to the changes of processing solutions is deteriorated by the lapse of time after coating of photographic material. As a result, in order to obtain a hard copy simply and rapidly with the performance constant at all times, a technique is required wherein the latent image formed from a silver halide emulsion having a high silver chloride content with high-intensity and short-time exposure is developed stably in as short a time period as possible.
As a light source for exposure of scanning exposure system recording apparatuses, for example, a glow lamp, a xenon lamp, a mercury lamp, a tungsten lamp, or a light-emitting diode is used conventionally. However, any of these light sources is attended with such practical defects as that the output is weak and the life is short. To circumvent these defects, there is a scanner that uses, as a light source for a scanning system, a coherent laser light source, for example a semiconductor laser or a gas laser, such as a He--Ne laser, an argon laser, and a He--Cd laser.
Gas lasers can provide high output, but they are attended with such defects as that they are large in size and expensive, and they require a modulator.
On the other hand, semiconductor lasers have such good points as that they are small in size and inexpensive; they can be modulated easily; and they have a longer life than gas lasers. The luminescence wavelength of these semiconductor lasers lies mainly in the range from the red region to the infrared region. When the semiconductor laser is used as a light source, the semiconductor laser may be used in two ways. One way combines a semiconductor laser with a non-linear optical element, to take out the visible second harmonics, so that a silver halide photographic material sensitized spectrally to visible radiation may be exposed to the light; the other way uses a semiconductor laser that can emit light ranging from red light to infrared light, so that a silver halide photographic material highly sensitive to the red/infrared region may be exposed to the light.
However, the conventional red/infrared-sensitive photographic material is unstable in latent image after exposure to light, and it is high in the change of photographic properties due to a change in the development processing, in comparison with photographic materials spectrally sensitized for blue/green. Further, in high-intensity exposure using a laser, the change of photographic properties due to a change in the development processing is increased further, and the change is far from optimal in practical application.
For such high-illumination scanning exposure, to minimize fluctuation of photographic properties due to changes in processing solutions, various techniques are known. For example, EP0350046 and JP-A ("JP-A" means unexamined published Japanese patent application) No. 18548/1990 disclose that, when silver halide emulsion grains high in silver chloride content are doped with metal ions (for example, ions of Fe, Rh, or Ir), fluctuation of photographic properties due to changes in processing solutions can be made small. Further, JP-A No. 15645/1992 discloses that, when a pivaloyl-type or benzoyl-type yellow coupler wherein the ortho position of the acetanilido in the molecule is substituted by an alkoxy group or the like is used, fluctuation of photographic properties due to changes in processing solutions can be made small. However, it cannot be said that even the use of these techniques is satisfactory, and the actual state is that the problem that fluctuation of photographic properties due to changes in processing solutions increases with the lapse of time during storage of unexposed photographic materials still remains unimproved.